The present invention comprises a cooling fin arrangement on a cooling fluid-receiving surface of an object made of heat conductive material such as a portion of a containment in which heat is produced and is to be dissipated by means of said fin arrangement, comprising a plurality of cooling fins in a manner so as to obtain that said fluid flow, at least partially, moves in between said cooling fins.
The present invention has applications to a great variety of such heat dissipating containments and will be described hereinafter for reasons of simplicity only with reference to a cover of a so-called viscous fan, it being understood that the present invention does not relate in particular to said viscous fan but to any type of heat dissipating containments which comprise cooling fins which favorise the transfer of the heat to a cooling fluid, which, in the case of the reference viscosity fan clutch will simply be the ambient air which impinges on the viscosity fan clutch during movement of the vehicle in which the fan is installed.
With reference to FIGS. 1 and 2 appended hereto, illustrating the prior art, FIG. 1 shows a typical fan assembly for a motor vehicle, comprising two concentric rings 2 and 3 between which a number of fan blades 4 are arranged in radial extension.
Axially inside thereof, the fan assembly comprises a viscosity clutch, from which only the cover 5 is visible, comprising a number of radially arranged cooling fins 6.
Typically this kind of fan arrangement is used in a vehicle in order to cool the cooling fluid of the engine, whereas the axis of the fan assembly is parallel to the length axis of the vehicle, however other arrangements may be envisaged.
Since the cooling power needed in order to cool a vehicle engine is dependent on operation conditions, such as outside temperature, ratio of vehicle speed to rotational speed of the engine and so forth, modern fan arrangements comprise a viscous clutch which transmits a variable momentum from the driving axis (not illustrated in FIG. 1) to the fan blades, whereby the operation of a viscosity clutch does not form part of the present invention and does not need to be described here in detail.
However in a few words, a viscosity clutch comprises two co-axial plates having a certain axial distance from each other, whereby this distance may be filled either with air, or with oil, and whereby the amount of oil present in the space between the two plates determines the ratio between input momentum and output momentum.
This type of viscosity clutch naturally produces heat, the so-called slip-heat, during its operation, which heat needs to be dissipated through the clutch cover 5 which carries radially arranged cooling fins 1 (see FIG. 2) spaced from each other by fluid channels 12.
FIG. 2 illustrates a perspective view of a portion of a clutch cover 5, as seen from a direction corresponding to arrow A of FIG. 1.
Naturally, the man of the art who designs a clutch cover for a viscosity clutch of the type as referred to above, will try to obtain the best possible heat transfer from the clutch cover to the surrounding air in order to improve the effectiveness of the clutch, and he will thus calculate the height, thickness, number and so forth of cooling fins on the surface of the clutch cover in a way as to optimise the heat transfer.
It is readily understandable that the heat transfer will be the better, the more cooling fins are present over the surface to be cooled, however, the present inventors have found that there is a limit of efficiency obtained by increasing the density of cooling fins.
Also, when a fluid flows along a smooth surface, irrespective of the overall configuration of the flow channel, a surface layer is being formed within which the flow is laminar.
The present invention, which has as objective to increase the heat transfer from, the cooling fins to the cooling fluid is therefore based on the discovery that on the one hand the heat transfer is enhanced if one changes from a laminar flow to a turbulent flow, and on the other hand, if one provides means which, although the present geometry would create a laminar flow, this geometry may be voluntarily modified in order to create a turbulent flow, within the above mentioned surface layer.
This object is achieved with a cooling fin arrangement according to the preamble of claim 1, characterized in that turbulence-creating formations are provided in said cooling fin arrangement so as to obtain a non-laminar flow of said cooling fluid within the above mentioned surface layer.
According to a particular embodiment of the present invention, these turbulence-creating formations may be protuberances of the surfaces of the cooling fins.
These protuberances may be formed integrally with the cooling fins, or be formed by wires or profiled bars which are fastened to the cool surfaces of the cooling fins by welding or the like and which extend perpendicular to the length dimension of said fins essentially perpendicular to the fluid flow.
In a particular embodiment of the present invention, said protuberances may comprise at least one embodiment which is oriented substantially perpendicular to the flow of the cooling fluid whereby the surface of said protuberances which is exposed to said fluid flow is arranged in angular relationship to said fluid flow.
The elevation of said protuberances above the surface of the cooling fins can of course be calculated so as to obtain a turbulent flow as soon as a certain fluid speed is achieved.
These protuberances may alternatively have the shape of individual balls or plates which are oriented perpendicular to the surface of the cooling fins but angled with respect to the fluid flow.
The present invention also relates to a containment of heat conductive material of or for a device which produces heat during its operation, wherein the outer surface of said containment comprises cooling fins which extend in any desired pattern over said outer surface and which represent a plurality of web-like structures. Said cooling fins, which are connected at one of their edges with said outer surface of said containment from where they extend in essentially perpendicular direction, comprise on at least one of there two flat surfaces turbulence-creating formations so as to obtain that the flow of the cooling fluid within the surface layer of the cooling fins created by more or less parallel webs, is turbulent.
As outlined at the beginning of the present description, the containment on which a cooling fin arrangement according to the present invention may be used, can be one of a variety of heat dissipating enclosures, whereas the cover of a viscous fan clutch of a vehicle fan arrangement is a typical example.
In this embodiment of a viscosity fan clutch of a vehicle the cooling fluid can be the ambient air which impinges during movement of the vehicle axially on the cover of the fan clutch, whereafter the air is led radially outwardly following trajectories formed between cooling fins which are arranged radially outwardly from a central point.